Dynamo-electric machine



' G. SCHROEDER DYNAMO ELE'JGTRIC MACHINE Sept. 14 1926.

Filed Sept. 9, 1924 2 Sheets-Sheet 1 Sept. 14 1926. 1,599,679

G. SCHROEDER DYNAMO ELECTRIC MACHINE Filed Sept. 9, 1924 v 2 Sheets$heet 2 Patented Sept. 14, 1926.

UNITED STATES PATENT OFFICE.

GIULIO SCHROEDER, OF WEST BYFLEET, ENG-LAND, ASSIGNOB. TO THE ENGLISH ELEC- TRIO COMPANY LIMITED, OF LONDON, ENGLAND, A'IBRITISH COMPANY.

DYNAMO-ELECTRIC MACHINE.

Application filed September 9, 1924, Serial No. 736,723, and in Great Britain September 19, 1923.

In certain types of dynamo electric machines having a winding distributed around the periphery of one element of the machine there exists the characteristic that, although the winding may be uniformly distributed, the current flowing therein is not uniform, being of a higher value in certain parts of the winding than in others. This want of uniformity is, in general, due to the fact that the winding carries two or more component currents differing in value or kind, this difference, in conjunction with the methods of leading the currents into and out of thewindings having the effect of producing resultant currents of high values in certain parts of the winding and low values in other parts.

An example of a machine element having the features above indicated is found in the armature of a synchronous rotary converter. In this case the turns of the winding adjacent to the tappings by which the alternating current circuits are connected with the armature carry heavier currents than the parts more remote from these points.

A result of this non-uniform distribution of current is the production of non-uniform heating of the machine, the output of which is of course limited by the temperature rise of the hottest point so that the output is lower for the generation of a given amount of heat in the case where this is distributed non-uniformly than in the case where an approximately uniform distribution exists. It is the object of the present invention to effect an improvement in the armature of a synchronous rotary converter by which the distribution of the heating is rendered more uniform. This improvement consists in arranging that the section of the conductor is varied from point to point around the core so that the greater section occurs where the higher efl'ective current values are found whereby the resistance loss taking place in the different. conductors is rendered more uniform. This grading of the section of the conductor with appropriate changes in the dimensions of the slots in cases where the winding is arranged in slots, will generall be done in steps in order to'comply wit ractical requirements, the number of steps eing limited by considerations of the relative advantage and ,costof-obtaining a more or less close approximation to uniform distribution of resistance losses.

Where this method of grading the section of the conductor is employed in connection with rotary converters having the armature winding arranged in slots of constant depth distributed around the core, the width of the slots will in general be varied in accordance with the grading of the conductor. In practice this may be carried out in two ways. In the one of these, particularly described here inafter, the pitch of the slots is as usual 'kept constant in value at all points on the core. In the other arrangement, which is dealt within the application of Barnes Serial No. 736,736, filed September 9, 1924, the pitch of the slots is varied from point to point around the core. The first arrangement has the effect of introducing a periodic variation in the reluctance of the path for the flux through any particular portion of a pole face as the armature moves past that region. For instance, in the case of a six phase rotary converter, the period of the variation in the local reluctance will be equal to one-third of the time occupied by the passage of any point on the periphery of the armature through a pole pitch. With such machines where short circuited windings are arranged on the pole faces for the purpose of damping or starting, it is necessary to take into consideration the presence of the disturbance in the flux produced b this periodic change of reluctance. Accor ingly a further object of this invention is to provide that the pole face winding is practically non-inductive to the flux pulsations produced in the manner indicated. This is effected by dividing the pole face windings into a series of independent short circuited sections, any oneof which contains only conductors which are so spaced on the pole face as to be non-inductively related to the periodic disturbance.

The invention will now be described by way of examplewith reference to Figures 1 to 5 of the accompanying drawin s.- Figure 1 shows diagrammatically an end View of a part of the slotted circumference of the and pole shoe of the associated field system with a damping winding situated in the pole shoe. Figure 2 shows a developed circumferential view of some of the armature slots as well as several armature coils placed in position therein. Figure 3 is a sectional view or one of the armature slots of a rotary converter not provided with a aded winding. Four conductors are shown in the slot. Figures 4: and show by comparison similar views of two slots and their associated conductors suitable for use in the armature of the same rotary converter after provid ng it with a graded armature winding arranged as in Figures 1 and 2.

In Figures 1 and 2 the (3-pole arn'iature is denoted by l and it has fifteen slots per pole. One of the six poles is denoted by 2 having a pole shoe 3 in which a suitable damping winding is arranged. The ninety armature slots are arranged around the armature circumference in eighteen groups of iive slots per group (each group occupysixty electrical degrees of the armature circu1nterence and three of each five are narrow slots and two are wide slots The armature winding scheme will be clear from an examination of Figure 2 wherein the wide conductors T, shown by heavy lines are arranged in the wid i its 5 this arrangement corresponds to Figure 5) and the narrow conductors 8 shown by light lines, are arranged in the narrow slots 4 (corresponding to Figure 4;). The wide conductors T are tapped at points 13 and it etc. at intervals of sixty electrical degrees around the winding and connected to six slip rings in the usual manner. The particular points at which the wide conductors are tapped depend upon the power factor, but with a leading power :t'actor which is the usual case in practice and with the type of winding shown those conductors which carry the largest currents in Figure 2 are those which lie in the direction of rotation of the armature from the tappin points. This is why most of the wide conductors are shown in Figure 2 to the leftof the tapping points, it being assumed that the armature rotates in the direction ot the arrow. The tappings 15 go in usual manner to the commutator segments.

In Figures 1 and 2 it will be observed that the pitch le gjth is the same between the centre lines oi any adjacent slots and this as previous 3* mentioned gives rise to a periodic variation in the reluctance of the path for the flux through any particular portion or a pole face as the armature moves past that region. To counteract the e'ttect of this varying reluctance tour independent short circuited squirrel cage windings are arranged in each pole shoe 3 and each of tiese windings has a pitch which cruses itto he nmi-indhctively related to the periodic disturluince or in other words such that the reluctance of the whole magnetic path through each winding remains invariable. ii Figure l the two bars 9, spaced sirt electrical degrees together with nnectors (not shown) form one of the L age dings and siinilarl the pairs ojt bars 10, 11 and 12 and their end connectors (not shown) term the three other i cage windings.

hat I claim as my invention and desire to secure by Lettes Patent is l. in a synchronous rotary converter an rmature winding having connectors leadto cmnniutator segments and serving for go of direct current and having tor the passage oi alternating curi the section or the conductors of which the armature winding is termed being \aried from point to point in the winding in such a way that the greater section is found near the points at which the tappings the alternating currents are located re the higher etl'ective current values QJLIEC.

2. .ln a synchronous rotary converter, an armature comprising a slotted core, a windi id slots having connectors leading segments and serving for c of direct current and having ipings JOl' the passage of alternating curthe section of the conductors of which mature winding is formed being i trozn point to point in the winding an L1 in such a way that the greater section is for .t s -v'ncln-on us rotary converter com n armature having a slotted core of unitorm pitch but different sod in similar recurring groups aaced around the core, a field lOI't circuited windings carried by the taco oi the ticld structure and consisting oi? independent sets of bars and separate connections associated with each of said and spaced on the taco oi the held structure so as to be non-inductively related to the periodic disturbance of flux producerii o the variation in the width of the slots.

5. A pol phase sym-hronous rotary coir 'tcr :ouiprisiug an armature having at d co e with slots ot uni form pitchbut width arranged in similar rccur groups, the recurrence taking place distances along the periphery of the core equal to a pole pitch divided by ciated with each of said sets, the bars in any half the number of phases of the alterone set being spaced apart from each other nating current side of the converter, by a distance equal to the pole pitch divided 10 a field structure, short circuited windby half the number of phases of the alternat- 5 ings carried by the face of said field ing current.

structure and consisting of independent sets In testimony whereof I affix my signature. of bars and separate end connections asso- GIULIO SCHROEDER. 

